Electrolytic condenser



Feb. 4, 1936. w. c. VAN GEEL ET! AL 2,029,451

ELECTROLYTIC CONDENSER Filed Feb. 25, 1932 INVENTORS WILLEM CHRISTIAANVAN GEEL BY 'HIEEIQMMENS ATTORNEY Patented. Feb. 4, 1936 UNITED STATES2,029,451 I nmoraow'nc oonnsnssa Willem Christiaan van Geei and HendrikEmmens, Eindhoven, Netherlands, assignors to Radio Corporation ofAmerica, a corporation oi Delaware Application February 25, 1932, SerialNo. 594,982 In the Netherlands June 20, 1931 5 Claims.

This invention relates to improvements in electric condensers.

It is an object of this invention to simplify and improve theconstruction of electrolytic condensers so that the life of thecondenser is increased.

In the customary construction of electrolytic condensers one electrodeof such a condenser consists of a metal plate or a metal wire coated byelectrolytic or chemical agency with an oxide coating and immersed in anelectrolyte constituting the other electrode. For this purpose theelectrolyte is furnished with a conductor for the supply of the electriccurrent, said conductor being formed, for example, by the wall of thevessel in which the electrolyte is enclosed.

One of the difliculties which have to be overcome with such condensersis the attack of the oxide coating so that the life of the condenser islimited.

Now it has been found that this attack is to be imputed to a largeextent to impurities enclosed in the electrolyte. Even when during themanufacture of the condenser a careful watch is kept that no impuritiesoccur in the electrolyte, it is found that in the course of time theynevertheless occur. Indeed, they are absorbed from the wall of thevessel or are due to the insulating parts which are used for taking theconductors through the wall of the vessel, said insulators containing ingeneral organic material.

Even when use is made of electrolytes consisting of solutions of solidsubstances in alcohol, such as glycerol, which electrolytes otherwisehave favourable properties with regard to leakage current and capacity,it is found that said disadvantage is not disposed of without additionalmeans.

This has only been found possible by using a solution of one or more ofthe primary or secondary phosphates in an alcohol, for example ofprimary potassium phosphate in glycerol. This combination has been foundto permit of the oxide coating of the metal electrodes being protectedfrom attack.

Perhaps this striking action is to be imputed to the circumstance thatit is found possible to dissolve a great deal of the solid substanceprimary potassium phosphate in the glycerol sothat consequently theproportion of the quantity of impurity in the liquid becomes negligiblerelatively to the quantity of the substance dissolved in addition andalso the influence of the impurities decreases thereby accordingly. Inthis case the circumstance that in spite of the large quantity ofprimary potassium phosphate which is dis- 5 solved the conductivity doesnot become great plays an important part since in most dissolvedsubstances in which the quantity of the substance dissolved iscomparatively large the conductivity of the electrolyte becomes great aswell and incl 10 dental thereto is an inadmissable leakage current.However, this phenomenon does not occur in the said use of primarypotassium phosphate.

Favourable results were obtained with a condenser one electrode of whichwas of aluminium, 15 whereas the electrolyte consisted of pure glycerol-having added to it 50 grams of primary potassium phosphate (KH2PO4) perliter.

Similarly, good results were obtained when this electrolyte had added toit in addition 10% of 20 water.

When, for example, a solution of primary potassium or sodium phosphateis used, this solution is acid. Now, a further protection of theelectrodes from attack can be obtained by adding to the solution abasicly reacting phosphate, for example secondary potassium or sodiumphosphate, in such a proportion that the solution is just neutral.

In order that the invention may be clearly understood and readilycarried into efiect a condenser in accordance therewith will now bedescribed more fully with reference to the accompanying drawing.

Referring to the drawing, a copper vessel l contains an electrolyte 2consisting of pure glycerol in which primary potassium phosphate isdissolved in a proportion of 50 grams per liter of glycerol. On itsupper side the vessel is closed by an ebonite disc 3 through which theend of an 40 aluminium wire 4 is taken. In order to obtain a largesurface area, the aluminium wire is wound helically. A plurality of suchhelices might be arranged one within the other. Leading-in wires may beconnected to 5 and 6. The aluminium wire is coated by chemical orelectrolytic agency with an oxide coating which constitutes theinsulating intermediate layer between the electrodes of the condenser.

A condenser as illustrated in the dram'ng is only suitable for smoothingdirect current as it disrupts the current only in one direction. It cantherefore be used as a rectifier as well. If such condensers are desiredto be used for alternating current, a second aluminium electrodesimilarly coated With an oxide coating may be arranged in theelectrolyte and the two aluminium electrodes may be connected to theterminals of the alternating current supply.

Various modifications are otherwise possible without departing from thescope of the invention. Thus, for example, the aluminium wire may beprofiled in order to increase the surface area and instead of wire usemay be made of rolled-up plates the windings of which are kept apart bydistance holders.

Alternatively, the electrolyte may have added to it over 10% of water.Even with of water good results have still beenobtained.

We claim:

1. An electrolytic condenser comprising a metallic electrode, an oxidecoating on said metallic electrode, an electrolyte consisting of asolution of acid phosphate, and alcohol of the group including glycerol,for the purpose of preventing an attack on said oxide coating.

2. An electrolytic condenser comprising a metallic electrode, an oxidecoating on said metallic electrode, and an electrolyte having theproperties of preventing an attack on the oxide coating of saidelectrode, consisting of a solution of primary potassium phosphate inglycerol to which solution is added substantially 10% of water.

3. An electrolytic condenser comprising a metallic electrode of alum numhaving an oxide coating, and an electroL'fie consisting of a solution ofpure glycerol in which primary potassium phosphate is dissolved in aquantity of grams per liter.

4. An electrolytic condenser comprising a copper vessel containing anelectrolyte of pure glycerol in which primary potassium phosphate isdissolved, an insulating disc enclosing said vessel, and an electrode ofaluminum wire having an oxide coating which constitutes an insulatinglayer between the condenser electrode.

5. An electrolytic rectifier comprising a copper vessel containing anelectrolyte of pure glycerol in which primary potassium phosphate isdissolved, an insulating disc enclosing said vessel, and two electrodesof aluminum wire having an oxide coating which constitutes an insulatinglayer between the rectifier electrodes.

WILLEM CHRISTIAAN VAN GEEL. HENDRIK EMMENS.

